1. Field of the Invention
This invention relates to a method of setting a density used for an image recording apparatus, such as a laser imager for drawing an image on a photosensitive material by performing laser-beam scanning, or the like.
2. Description of the Prior Art
Recently, in the medical field, various techniques, such as CT (computed tomography), MR (magnetic resonance) and the like, have been used for observing the interior of a human body. Those techniques require high-definition images. In accordance with the development of such techniques, it has become necessary to record images obtained by these techniques without imparing the picture quality of the images. A laser imager is an apparatus which stores an image by digitizing the image for every picture element and performs recording by scanning a photosensitive member while modulating a laser beam with an intensity proportional to the digitized value of each picture element. The laser imager has an advantage in that, since the image is stored as digital values for every picture element, it is always possible to record a halftone stable image with a simple operation by performing image processing, such as gradation correction and the like. At present, a recorded image having the highest picture quality is obtained by performing recording on a transparent silver-halide film using the laser imager.
When changing the maximum density value of a photosensitive material in accordance with an object for an image, or the taste of an observer, if a method of suppressing the maximum intensity of a laser beam by directly modulating the laser beam is adopted, the dynamic range of the modulated light is reduced, particularly in the case of using a semiconductor laser light source. Hence, a desired gradation accuracy cannot be obtained. Accordingly, in general, as disclosed in Japanese Patent Application Public Disclosure (Kokai) No. 60-250327 (1985), the maximum intensity of a laser beam is optically changed by disposing a filter or the like in the optical path of the beam. For example, a polarizer is used as the filter, and the intensity of the laser beam passing through the polarizer is changed by rotating the polarizer using a dial for adjusting the density of a silver-halide film.
In the above-described conventional approach, however, the density of an image recorded on the photosensitive material is not exactly proportional to the intensity of the projected laser beam, and is greatly influenced by the environment, such as temperature and the like. Another influence is the kind of developer to be used. Hence, it is necessary to adjust the graduation of the dial for adjusting the density at a location where the laser imager is used. Conventionally, a complicated method has been adopted such that a test image is recorded and developed on a photosensitive material while the dial for adjustment is rotated to different angles, and the graduation of the dial is calibrated by measuring the densities of the recorded image. Accordingly, a method of setting the density of a photosensitive material in a simple manner is needed.